In a semiconductor device package assembly, a semiconductor die (also referred to as a semiconductor integrated circuit (IC) chip or “chip”) may be bonded directly to a package substrate. Such a die may be formed with solder bumps affixed to its respective input-output (I/O) bonding pads. During packaging, the die may be “flipped” onto its front surface (e.g., active circuit surface) so that the solder bumps form electrical and mechanical connections directly between the die and conductive metal pads on the package substrate. Underfill is generally applied between the gap formed by the solder bumps in order to further secure the die to the package substrate. A heat spreading lid is then attached over the die. A semiconductor device package of this type is commonly called a flip-chip package.
When electrical current flows through the semiconductor die, the semiconductor die generates heat. As such, passive and active thermal management devices are used to minimize potential damaging effects from heat on the device. Such thermal management devices include heat spreading lids and heat sinks. Heat conducting material may also be used to facilitate heat transfer in the package. Typically, a heat conducting material such as a thermal interface material (TIM) is deposited between the die and the heat spreading lid to enhance heat transfer from the die to the heat spreading lid.
However, device packages using TIM may have problems meeting heat dissipation requirements. Firstly, the thermal conductance of TIM is substantially lower than that of a good thermal conducting metal such as copper, which may result in lower efficiency of heat transfer. For example, the thermal conductivity of an exemplary TIM is approximately 3.8 watts per meter kelvin (W/m-k) while the thermal conductivity of copper is approximately 385 W/m-k. Secondly, the conventional lid attach process uses the package substrate as a physical limiter or stopper to prevent the heat spreading lid from crushing the die. This may cause the layer of TIM between the die and the heat spreading lid to have an inconsistent thickness, which may eventually lead to heat dissipation problems during device operation.